There used to be a bottled Islay water drawn from a source which filtered through peat - it was brown and looked pretty unappetising, but it was great for adding to peaty malts from Islay or anywhere else. I haven't seen it around for quite some time, though, and as Ize says, not worth paying to ship all the way to Finland or Sweden... I find that plain ordinary London tap does the job adequately if there isn't anything else, and you lucky Scandinavians are probably blessed with better water than that from your own taps. I tend to dilute to a bit above 40%, but do it gradually, tasting along the way. With some malts, the flavour development is remarkable - Lagavulin seems to get stronger as it gets diluted, I suppose because the alcohol content gets less dominant and the peaty elements get a chance to come through.
I didn't quite get the comment about resting the whisky in a bottle - is that after diluting? I've never tried that, but I do get the impression that when diluting in a glass, the water seems to bring out the aromas strongly but dissipate them quickly too, so you should finish the glass reasonably quickly. Not that that is usually a problem...
